The commonsense fallacy

Get up early, when it is yet dark, and go to a place where you have a wide view. Look to the east, and then, yes, you’ll see the sun rise. Or rather that’s the way it seems to you, for actually it is not so that the sun rises, but it is the earth that goes down. The earth rotates on its axis and every time the point where you are turns to the side where the sun is, the sun comes in your field of view. Then it seems to you as if the sun rises, though in fact the sun doesn’t move, but the point where you are “rises”, so to speak, i.e. it moves so that the sun becomes visible. Nowadays, this is what everybody (or most of us) knows. It’s commonsense. That the sun “rises” is merely an old-fashioned way of speaking. Nonetheless, once there was a time that everybody on earth thought that the sun really rises. That it was not a kind of metaphor but that it was a fact. You could even be killed if you dared to assert that it was not. Then it was commonsense that the sun really rises.
What this case illustrates is that commonsense ideas may not be reliable. They are generally accepted but this doesn’t mean that they are true knowledge. They are just views based on how things appear and on what is commonly accepted. However, it’s often important to have reliable knowledge and that’s why we have developed science: a method to get reliable knowledge based on sound reasoning plus ways to test whether statements about possible facts are true. (As you see here, I think that the essence of science is in the method, not in the facts, as many people think). In spite of this it often happens that people say that a statement is true or that something is a fact, merely because it is “commonsense”, or because “everybody knows”, or, as we say in Dutch, because it is a matter of “healthy reasoning”. Such an appeal to commonsense is called the “commonsense fallacy” (CSF), or, as the case may be, an “appeal to the people fallacy” “argument from popularity”, “argument from tradition”, and the like. Although there are slight differences between these fallacies, I treat them here as if they are all varieties of the commonsense fallacy. Of course, commonsense can be true. For example, the scientific explanation of sunrise has become commonsense, as we have seen. Therefore, I must further explain what the commonsense fallacy involves:
Committing the commonsense fallacy is “asserting that your conclusion or facts are just ‘commonsense’ when, in fact, they are not. We must argue as to why we believe something is commonsense if there is any doubt that the belief is not common, rather than just asserting that it is. This is a more specific version of alleged certainty.” (source) Or let me quote a little bit more from the same source:
The logical form of CSF is:
                                        It’s commonsense that X is true.
                                        Therefore, X is true
Example: It's commonsense that if you smack your children, they will stop the bad behaviour. So don't tell me not to hit my kids.
Explanation: What is often accepted as “commonsense” is factually incorrect or otherwise problematic. While hitting your kids may stop their current bad behaviour, the long-term psychological and behavioural negative effects can far outweigh the temporary benefits. Logically speaking, the example simply appeals to “commonsense” rather than makes an attempt at a strong argument. (more examples in this same source)The source of the idea that commonsense is true because it is something that “everybody” knows is the wrong idea that what seems true to you or true to many must be true just for that reason. However, each person has his or her own individual experiences and beliefs, and, in addition, groups of people, if not whole cultures, have often common or equal experiences and beliefs. So, what seems right to one person may not seem right to everyone, and what seems right to one group or even culture may not seem right to others, who belong to other groups or cultures. When one person, group or culture accepts a view that others don’t, it’s usually due to a difference in their views of the world and internalized ideologies rather than an intellectual deficit or incapacity to reason. But so long as beliefs are based simply on commonsense and aren’t supported by evidence, they aren’t reliable. So if an assertion or statement is not more than that and not (implicitly) based on evidence but merely based on an appeal to commonsense, it’s a case of the commonsense fallacy. Beliefs that rely on the ambiguous concept of something being self-evident can change according to personal, group or cultural experiences. (see also here) However, what once was dubious commonsense can become evidence-based commonsense, as the sunrise example shows.